As an example of a table that is somewhat less than accessible, consider the article w:Hydrogen. This, like many other articles on elements in the periodic table, has a large table detailing many of its characteristics. The tables are color-coded (which is good), and look very nice in a graphical browser with a large screen, but in Lynx, here's how it turns out:

It's still relatively readable, but it could be better. In particular, because the "headings" within the table ("General", "Atomic Properties", etc.) are not actually marked up as headings (using h2 or the appropriate Wikipedia code), they are not rendered that way, and it's hard to tell that they are, in fact, headings.

There is also the fact that the table is rendered before the contents of the article. Accessibility experts usually recommend including some kind of link at the top of a lengthy block of stuff like this, so that users who are accessing the page sequentially (not random-access, as those with a visual browser and mouse do) can skip past all of it to go right to the article itself.

Whether either of these things can be easily implemented in the current framework of our PHP code and the available stylesheets, I do not know. Tables like this may benefit from a basic simplification process; in particular, it should be relatively easy to add CSS descriptors for the colors, headings, alignment and stuff that tables like this use. Much of this table's contents could then be rendered inside a div or other block element, with h2 or something for the headings, and lists for many of the additional bits. Some of it, maybe even all of it, may be best rendered inside a table, but a considerable amount of simplification could be done.

The following is perhaps a better approach to tables such as this one. It's far from perfect, but I think it's easier to edit (and looks better, particularly in a text browser) than the existing one. I do not know if it is more accessible, but with additional work I think it has the potential to be more accessible. (Ignore all the broken links; this was intended to be in the regular Wikipedia namespace. The table is what is important here.)

Most Stable Isotopes

Hydrogen is a chemical element in the periodic table that has the symbol H and atomic number 1. A colorless, odorless, non-metal, univalent, highly flammable diatomic gas, hydrogen is the lightest and most abundant element in the universe and is present in water and in all organic compounds and living organisms. Hydrogen is able to chemically react with most elements. Stars in their main sequence are overwhelmingly composed of hydrogen in its plasma state. This element is used in ammonia production, as a lifting gas, an alternative fuel, and more recently as a power-source of fuel cells.

Hydrogen is the lightest chemical element with its most common isotope consisting of just a single proton and electron. At standard temperature and pressure conditions, hydrogen forms a diatomicgas, H2, with a boiling point of only 20.27 K and a melting point of 14.02 K. Under exceedingly high pressures, like those found at the center of gas giants, the molecules lose their identity and the hydrogen becomes a liquid metal. Under the exceedingly low pressure conditions found in space, hydrogen tends to exist as individual atoms, simply because there is no way for them to combine; clouds of H2 form and are associated with star formation.

It is fourteen and a half times lighter than air and at one time was widely used as a lifting agent in balloons and zeppelins until the Hindenburg disaster convinced the public that the gas was too dangerous for this purpose.

Hydrogen is the most abundant element in the universe, making up 75% of normal matter by mass and over 90% by number of atoms. This element is found in great abundance stars and gas giant planets. Relative to its great abundance elsewhere, hydrogen is very rare in the earth's atmosphere (1 ppm by volume). The most common source for this element on earth is water which is composed two parts hydrogen to one part oxygen (H2O). Other sources are; most forms of organic matter which includes all known life forms, coal, fossil fuels and natural gas. Methane (CH4), which is a byproduct of organic decay, is an increasingly important source of hydrogen.

It's definitely better, in my opinion. The headings help break the table up a bit, and make it obvious what is being covered in each section of the table. Formatting it as a list has the added benefit that the cell contents aren't mashed together in a text-only or speech environment. The last (previously nested) table is still somewhat jumbled, but that's the kind of thing that probably should be in a table.

The Wikipedia articles on various U.S. states follow a similar table-formatted structure. These have quirks of their own, it seems, one of which is the fact that line breaks are used to create separated "headings" within table cells. Visually, it usually seems to work alright, but it's another example of straining a rendering quirk to make it perform a semantic job it wasn't made to do, when there are perfectly acceptable semantic structures for doing this job. Let me just illustrate. Here is what the table portion of w:Texas looks like in Lynx:

This may very well be a bug in Lynx; line breaks within table cells should probably not cause this to happen, but there it is. The problem is, we're relying on line breaks to appropriately align a "heading" with its "contents." Such a format was likely chosen to avoid having a border around each cell, but this is something that could be fixed if we got clever with our CSS.